Stone matrix asphalt (SMA), also known as stone mastic asphalt, is a tough, stable rut-resistant asphalt mixture that relies on stone-to-stone contact to provide strength and a rich mortar binder to provide durability. These objectives are usually achieved with a gap-graded aggregate coupled with fiber or polymer modified, and high asphalt content mixture. The SMA is composed of aggregate(s), mineral filler, asphalt cement and stabilizer. In general, the SMA mixture contains 6%-10% by weight of mineral filler.
Mineral filler is a finely divided mineral matter such as rock dust, slag dust, hydrated lime, hydraulic cement, fly ash, loess, or other suitable mineral matter. Mineral filler is graded within the following limits, per ASTM D 242-95 and AASHTO M17 Standards:
SievePercent Passing (by mass)600 μm (No. 30)100300 μm (No. 50)95-100 75 μm (No. 30)70-100
While a variety of materials can be used as mineral filler in SMA, fly ash and rock dust are believed to be the most common.
Attempts to use lime kiln dust as a mineral filler in SMA have been made but many have been unsatisfactory and no certainty is available as to how to provide an operative system.